chapter01.js

function splat(fun) {
  return function(array) {
    return fun.apply(null, array);
  };
}

var addArrayElements = splat(function(x, y) { return x + y });

addArrayElements([1, 2]);
//=> 3

function unsplat(fun) {
  return function() {
    return fun.call(null, _.toArray(arguments));
  };
}

var joinElements = unsplat(function(array) { return array.join(' ') });

joinElements(1, 2);
//=> "1 2"

joinElements('-', '$', '/', '!', ':');
//=> "- $ / ! :"

function parseAge(age) {
  if (!_.isString(age)) throw new Error("Expecting a string");
  var a;

  console.log("Attempting to parse an age");

  a = parseInt(age, 10);

  if (_.isNaN(a)) {
    console.log(["Could not parse age:", age].join(' '));
    a = 0;
  }

  return a;
}

function fail(thing) {
  throw new Error(thing);
}

function warn(thing) {
  console.log(["WARNING:", thing].join(' '));
}

function note(thing) {
  console.log(["NOTE:", thing].join(' '));
}

function parseAge(age) {
  if (!_.isString(age)) fail("Expecting a string");
  var a;

  note("Attempting to parse an age");
  a = parseInt(age, 10);

  if (_.isNaN(a)) {
    warn(["Could not parse age:", age].join(' '));
    a = 0;
  }

  return a;
}

var letters = ['a', 'b', 'c'];

letters[1];
//=> 'b'

function naiveNth(a, index) {
  return a[index];
}

function isIndexed(data) {
  return _.isArray(data) || _.isString(data);
}

function nth(a, index) {
  if (!_.isNumber(index)) fail("Expected a number as the index");
  if (!isIndexed(a)) fail("Not supported on non-indexed type");
  if ((index < 0) || (index > a.length - 1))
    fail("Index value is out of bounds");

  return a[index];
}

function second(a) {
  return nth(a, 1);
}

function compareLessThanOrEqual(x, y) {
  if (x < y) return -1;
  if (y < x) return  1;
  return 0;
}

[2, 3, -1, -6, 0, -108, 42, 10].sort(compareLessThanOrEqual);
//=> [-108, -6, -1, 0, 2, 3, 10, 42]

function lessOrEqual(x, y) {
  return x <= y;
}

function comparator(pred) {
  return function(x, y) {
    if (truthy(pred(x, y)))
      return -1;
    else if (truthy(pred(y, x)))
      return 1;
    else
      return 0;
  };
};

function lameCSV(str) {
  return _.reduce(str.split("\n"), function(table, row) {
    table.push(_.map(row.split(","), function(c) { return c.trim()}));
    return table;
  }, []);
};

var peopleTable = lameCSV("name,age,hair\nMerble,35,red\nBob,64,blonde");

peopleTable;
//=> [["name",  "age",  "hair"],
//    ["Merble", "35",  "red"],
//    ["Bob",    "64",  "blonde"]]

function selectNames(table) {
  return _.rest(_.map(table, _.first));
}

function selectAges(table) {
  return _.rest(_.map(table, second));
}

function selectHairColor(table) {
  return _.rest(_.map(table, function(row) {
    return nth(row, 2);
  }));
}

var mergeResults = _.zip;

function existy(x) { return x != null };

function truthy(x) { return (x !== false) && existy(x) };

function doWhen(cond, action) {
  if(truthy(cond))
    return action();
  else
    return undefined;
}

function executeIfHasField(target, name) {
  return doWhen(existy(target[name]), function() {
    var result = _.result(target, name);
    console.log(['The result is', result].join(' '));
    return result;
  });
}